By measuring changes in salinity on the ocean’s surface, the researchers inferred that the water cycle had accelerated by about 4 percent over the last half-century. That does not sound particularly large, but it is twice the figure generated from computerized analyses of the climate.

If the estimate holds up, it implies that the water cycle could quicken by as much as 20 percent later in this century as the planet warms, potentially leading to more droughts and floods.

“This provides another piece of independent evidence that we need to start taking the problem of global warming seriously,” said Paul J. Durack, a researcher at the Lawrence Livermore National Laboratory in California and the lead author of a paper being published Friday in the journal Science.